Which organism is most commonly associated with bacterial sinusitis?

• A. Escherichia coli
• B. Streptococcus pneumoniae
• C. Haemophilus influenzae
• D. Staphylococcus aureus

Answer: (B)

Streptococcus pneumoniae is the organism most commonly associated with bacterial sinusitis. Sinusitis often follows a viral upper respiratory infection that impairs mucociliary clearance, allowing typical nasopharyngeal bacteria to overgrow. Among the usual suspects—Streptococcus pneumoniae, non-typable Haemophilus influenzae, and Moraxella catarrhalis—Streptococcus pneumoniae has historically been the leading cause across both adults and children, which is why it’s the best choice.

Haemophilus influenzae is also a frequent offender, especially in children, and Moraxella catarrhalis commonly appears as well, but they’re typically secondary to the top pathogen. Other organisms like Escherichia coli are not typical residents of the sinus flora, and Staphylococcus aureus is less common in uncomplicated acute sinusitis, more often emerging in specific contexts such as post-viral complications or chronic/hospital-associated cases.